The present invention is concerned with improved solar heaters of the general type described in my prior U.S. Pat. No. 3,919,998 issued Nov. 18, 1975, for "Convection-Type Solar Heating Unit". The solar heater of my said prior patent is based upon the principle that radiated solar energy falling on an absorbing body, e.g., a steam boiler disposed within the solar heating unit, would heat the boiler to an extremely high temperature if the boiler did not lose heat by re-radiation and conduction. Such conduction and re-radiation is effectively minimized by so arranging various surfaces in the solar heater that they radiate less than they absorb, and the conduction loss which would otherwise occur is eliminated by the use of solar radiation absorbing sheets that heat the air surrounding the boiler to a temperature as high as or higher than the temperature of the heated boiler.
Since the basic structural considerations which should be embodied in a solar heater achieving these results are fully described in my said prior U.S. Pat. No. 3,919,998, the disclosure of said prior patent is incorporated herein by reference. Briefly, the solar heating unit comprises a plurality of containers, i.e., two or more containers, nested one within the other with each of said containers having a gaseous medium, e.g., air therein. The containers respectively have transparent upper surfaces which are superposed and positioned to admit solar radiation to each of said containers. In addition each container houses one or more solar radiation absorbing sheets which transfer heat to the gaseous medium within the container. Various different other surfaces of the containers are coated with heat insulating and with heat reflective materials. The heat radiating sheets are so arranged that convection currents are produced in the gaseous medium within the containers thereby to cause the temperature of the gaseous medium in the innermost container to be raised to a temperature which converts water to steam, and a steam boiler structure is provided within the innermost container to achieve this conversion.
As discussed in my prior patent, the overall efficiency of a solar heating system is measured by the heat units (BTU's) obtainable per dollar invested, and in evaluating the comparative efficiencies of solar heating systems, therefore, the most practical system becomes one that generates the greatest useful energy output per dollar invested. A primary purpose of my prior patented invention was, accordingly, to provide a solar heating system which made use throughout of comparatively inexpensive components and which, moreover, permitted the elimination of auxiliary devices that would increase the cost of the solar heating unit. These cost considerations are equally relevant in respect to the steam boiler itself, for the use of a boiler configuration which is expensive to construct would reduce the overall efficiency of the heating system. Nevertheless, the boiler structure must be of such configuration that it is adapted for incorporation into a solar heating system of the type described, and exhibits adequate strength to resist the very significant internal pressures which are produced as steam is generated. The present invention accomplishes these results and, in addition, provides a number of further improvements which individually and cooperatively improve the overall efficiency of solar heating systems of the general type described in my aforesaid prior patent.